Method and apparatus for transferring toner from carrying member to image bearing member using chains of magnetic particles

Abstract

A developing method including forming a layer of electrically charged toner particles on a surface of the developer carrying member and dispersing magnetic particles retaining on their surfaces electrically charged toner particles on the surface of the developer carrying member, carrying the particles on the developer carrying member to a developing position where a surface of an electrostatic latent image bearing member for bearing an electrostatic latent image is opposed with a clearance to the surface of the developer carrying member, applying an alternating electric field across the clearance and forming the magnetic particles into chains of the magnetic particles by magnetic field generating means disposed behind the developer carrying member, and developing the electrostatic latent image by the charged toner particles on the surface of the developer carrying member and on the surfaces of the magnetic particles.

What is claimed is: 
     
       1. A developing method, comprising: forming a layer of electrically charged toner particles on a surface of a developer carrying member and dispersing magnetic particles retaining on their surfaces electrically charged toner particles on the surface of the developer carrying member;   carrying said toner particles and magnetic particles on the developer carrying member to a developing position where a surface of an electrostatic latent image bearing member for bearing an electrostatic latent image is opposed with a clearance to the surface of the developer carrying member;   forming at the developing position a alternating electric field against said electrostatic image and forming chains of magnetic particles extending toward and contacting the image bearing member at the developing position by stationary magnetic field generating means disposed behind the developer carrying member surface; and   developing the electrostatic latent image by the charged toner particles on the surface of the developer carrying member and on the surfaces of the magnetic particles in the clearance under said alternating electric field and said stationary magnetic field.   
     
     
       2. A method according to claim 1, wherein the chains of the magnetic particles are contacted to the electrostatic latent image bearing member at the developing position, and wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       3. A method according to claim 2, wherein the volumetric ratio Vd is 2.6-26%. 
     
     
       4. A method according to claim 2, wherein a total weight of the toner particles in the toner particle layer on the surface of the developer carrying member and the toner particles on the surfaces of the magnetic particles at the developing station is 4-40 % of a weight of the magnetic particles in the developing position. 
     
     
       5. A method according to claim 2, wherein an amount of the developer carried on the developer carrying member including the toner particle layer, the toner particles on the surfaces of the magnetic particles and the magnetic particles is 0.5×10 -2  - 5×10 -2  g/cm 2 . 
     
     
       6. A method according to claim 4, wherein an amount of the developer carried on the developer carrying member including the toner particle layer, the toner particles on the surfaces of the magnetic particles and the magnetic particles is 0.5×10 31  2 - 5×10 -2  g/cm 2 . 
     
     
       7. A method according to claim 2, wherein the toner particle layer, the toner particles on the surfaces of the magnetic particles and the magnetic particles carried to the developing position is applied onto the surface of the developer carrying member from a developer container containing mixed toner particles and magnetic particles, with a regulation by a developer regulating member disposed opposed to the surface of the developer carrying member, and wherein said volumetric ratio Vd and a volumetric ratio V of the magnetic particles in a region immediately before the developer goes out of the container, satisfy:   0.1≦Vd/V≦1.0.     
     
     
       8. A method according to claim 7, wherein Vd/V satisfied 0.2≦Vd/V≦0.8. 
     
     
       9. A method according to claim 7, wherein volumetric ratio V is not less than 20%. 
     
     
       10. A method according to claim 1, wherein an amount of the charged toner particles in the toner particle layer is not less than 0.05×10 -3  g/cm 2  and not more than 1.0×10 -3  g/cm 2 . 
     
     
       11. A method according to claim 10, wherein an amount of the toner particles in the toner particle layer is not less than 0.1×10 -3  g/cm 2  and not more than 0.6×10 -3  g/cm 2 . 
     
     
       12. A method according to claim 10, wherein a thickness of the toner particle layer is 1/50-1/5 of the clearance between the surface of the electrostatic latent image bearing member and the surface of the developer carrying member at the developing position. 
     
     
       13. A method according to claim 10, wherein the chains of the magnetic particles are contacted to the electrostatic latent image bearing member at the developing position, and wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       14. A method according to claim 1, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       15. A method according to claim 14, wherein the weight ratio is 1:1-1:5. 
     
     
       16. A method according to claim 14, wherein the chains of the magnetic particles are contacted to the electrostatic latent image bearing member at the developing position, and wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       17. A method according to claim 10, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       18. A method according to claim 1, wherein a peripheral speed of movement of the developer carrying member is 0.8-1.5 times a peripheral speed of movement of the electrostatic latent image bearing member. 
     
     
       19. A method according to claim 18, wherein the chains of the magnetic particles are contacted to the electrostatic latent image bearing member at the developing position, and wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing station, is 1.5-30%. 
     
     
       20. A developing method, comprising: carrying magnetic particles and toner particles on a developer carrying member which is closely opposed to an electrostatic latent image bearing member;   forming an alternating electric field at a developing position where the electrostatic latent image bearing member and the developer carrying member are closely opposed to transfer the toner particles carried on said developer carrying member and the toner particles carried on the chains of the magnetic particles to the electrostatic latent image bearing member;   wherein the following is satisfied:   g 2  -g 1  >0.25   where g 1  is a clearance between the latent image bearing member and the developer carrying member measured along the line G1 connecting a closest points therebetween,   g 2  is a clearance between the latent image bearing member and the developer carrying member measured along a line G2 which is parallel with and spaced 2 mm from line G1.   
     
     
       21. A method according to claim 20, wherein g 2  - g 1  >0.34. 
     
     
       22. A method according to claim 20, a peripheral speed of movement of the surface of the electrostatic latent image bearing member is 150-400 mm/sec. 
     
     
       23. A method according to claim 20, wherein the magnetic particles are contacted to the electrostatic latent image bearing member at the developing position, and wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       24. A method according to claim 1, wherein said magnetic particles are each ferrite particle coated with resin. 
     
     
       25. A method according to claim 8, wherein said magnetic particles are each ferrite particle coated with resin. 
     
     
       26. A method according to claim 20, wherein said magnetic particles are each ferrite particle coated with resin. 
     
     
       27. A developing apparatus for developing an electrostatic latent image on an electrostatic latent image bearing member, comprising: a container for containing a developer comprising toner particles and magnetic particles;   a developer carrying member opposed to the electrostatic latent image bearing member for forming a developing position for supplying the toner particles to the latent image bearing member and for carrying the developer from said container to the developing position;   first magnetic field generating means disposed across said developer carrying member from the latent image bearing member for generating a magnetic field to contact the magnetic particles to the latent image bearing member at the developing position;   developer regulating member disposed upstream of the developing position with respect to movement of a surface of said developer carrying member and spaced apart from the surface of said developer carrying member for regulating the developer carried to the developing position;   second magnetic field generating means disposed across said developer carrying member from said regulating member and disposed upstream of said developer regulating member with respect to the movement; and alternating electric field generating means for forming an alternating electric field at the developing position to transfer toner particles carried on a surface of said developer carrying member and the toner particles carried on surfaces of the magnetic particles to the latent image bearing member;   wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position is from 1.5 to 30%.   
     
     
       28. An apparatus according to claim 27, further comprising developer circulation limiting means disposed upstream of said regulating member with respect to the movement and cooperable with said developer carrying means to form a clearance therewith having a sectional area gradually decreasing toward said regulating member from an upstream side, wherein said second magnetic field means is opposed to said limiting member. 
     
     
       29. An apparatus according to claim 28, wherein an angle θ formed between a regulating portion of said developer regulating member and said second magnetic field generating means as seen from a center of rotation of said developer carrying member is not less than 2 degrees and not more than 40 degrees. 
     
     
       30. An apparatus according to claim 28, wherein in a region defined by said limiting member and said developer carrying member, an amount of the magnetic particles is larger than that in the other region in said developer container, and wherein a volumetric ratio V of the magnetic particles in the defined region satisfies: 0.1≦Vd/V≦1.0. 
     
     
       31. An apparatus according to claim 27, wherein an amount of the toner particles applied on said developer carrying member is not less than 0.05×10 -3  g/cm 2  and not more than 1.0×10 -3  g/cm 2 . 
     
     
       32. An apparatus according to claim 28, wherein an amount of the toner particles applied on said developer carrying member is not less than 0.05×10 -3  g/cm 2  and not more than 1.0×10 -3  g/cm 2 . 
     
     
       33. A method according to claim 27, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       34. A method according to claim 28, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       35. A method according to claim 31, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       36. A method according to claim 32, wherein a weight ratio between the toner particles in the toner particle layer and the toner particles on the surfaces of the magnetic particles is 2:1-1:10. 
     
     
       37. A developing apparatus for developing an electrostatic latent image on an electrostatic latent image bearing member, comprising: a container for containing a developer comprising toner particles and magnetic particles;   a developer carrying member opposed to the electrostatic latent image bearing member for forming a developing position for supplying the toner particles to the latent image bearing member and for carrying the developer from said container to the developing position;   first magnetic field generating means disposed across said developer carrying member from the latent image bearing member for generating a magnetic field for forming chains of magnetic particles extending toward and contacting the image bearing member at the developing position;   developer regulating member disposed upstream of the developing position with respect to movement of a surface of said developer carrying member for regulating the developer carried to the developing position;   second magnetic field generating means disposed across said developer carrying member from said regulating member and disposed upstream of said developer regulating member with respect to the movement; and a guiding member having a surface for guiding the developer, the guiding surface forming with said developer carrying member a clearance which gradually decreases from an upstream side of said developer regulating means with respect to the movement toward said developer regulating means, wherein said second magnetic field generating means has a maximum magnetic field generating portion which is opposed to the developer guiding surface; and   alternating electric field generating means for forming an alternating electric field at the developing position to transfer the toner particle carried on said developer carrying member and on the chains of the magnetic particles to the latent image bearing member.   
     
     
       38. An apparatus according to claim 37, wherein said developer regulating means and said guiding member are integrally formed, and wherein a length of the guiding surface measured along a direction of the movement is not less than 5 mm and not more than 15 mm. 
     
     
       39. An apparatus according to claim 37, wherein said guiding surface is disposed above a horizontal plane including a rotational axis of said developer carrying member, and extends across a vertical plane including the rotational axis. 
     
     
       40. An apparatus according to claim 39, wherein said developer regulating means is disposed in that quadrant in coordinates defined by the horizontal and vertical planes which is above the horizontal plane and in which movement of the surface of said developer carrying member contains a downward component, and said developer regulating means has a regulating edge spaced from the surface of said developer carrying member, wherein an angle between the guiding surface and a tangential plane to the surface of said developer carrying member at a position where the regulating edge is opposed to the surface, measured from the tangential plane in a direction upwardly away therefrom is more than 0 degree and not more than 45 degrees. 
     
     
       41. An apparatus according to claim 37, wherein said second magnetic field generating means is a magnetic pole providing a maximum magnetic flux density of not less than 600 Gausses, and wherein an angle formed between a position where the maximum magnetic flux density is formed and that end of the guiding surface which is upstream with respect to the movement as seen from a rotational axis of said developer carrying member is not less than 5 degrees. 
     
     
       42. An apparatus according to claim 40, wherein said second magnetic field generating means is a magnetic pole providing a maximum magnetic flux density of not less than 600 Gausses, and wherein an angle formed between a position where the maximum magnetic flux density is formed and that end of the guiding surface which is upstream with respect to the movement as seen from a rotational axis of said developer carrying member is not less than 5 degrees. 
     
     
       43. An apparatus according to claim 37, wherein the clearance formed between the guiding surface and the surface of said developer carrying member is larger than the clearance formed between the regulating edge of said developer regulating means and the surface of the developer carrying member, and wherein said guiding member and said developer regulating means are integral. 
     
     
       44. An apparatus according to claim 43, wherein said developer regulating means includes a non-magnetic blade, and wherein said guiding member includes a magnetic member adjacent said non-magnetic blade, and wherein said second magnetic field generating means is disposed upstream of said magnetic member with respect to the movement. 
     
     
       45. An apparatus according to claim 41, wherein a volumetric ratio of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       46. An apparatus according to claim 44, wherein a volumetric ratio of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position, is 1.5-30%. 
     
     
       47. A developing method, comprising: forming a layer of electrically charged toner particles on a surface of a rotatable developer carrying cylindrical sleeve and dispersing magnetic particles retaining on their surfaces electrically charged toner particles on the surface of the cylindrical sleeve;   carrying said toner particles and magnetic particles on the cylindrical sleeve to a developing position where a surface of a rotatable electrostatic latent image bearing drum for bearing an electrostatic latent image is opposed with a clearance to the surface of the cylindrical sleeve;   forming at the developing position an electric field having alternately changing directions and forming at the developing position the magnetic particles into chains by stationary magnetic field generating means disposed in said cylindrical sleeve, wherein the chains extend toward and contact the drum; and   developing the electrostatic latent image by the charged toner particles on the surface of the cylindrical sleeve and on the surfaces of the magnetic particles in the clearance under said alternating electric field and said stationary magnetic field.   
     
     
       48. A method according to claim 47, wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing drum and the developer carrying sleeve at the developing position is 1.5-30%. 
     
     
       49. A method according to claim 47 or 48, wherein from 0.5×10 -2  -5×10 -2  g/cm 2  of developer is carried on the developer carrying sleeve including the toner particle layer, the toner particles on the surfaces of the magnetic particles and the magnetic particles. 
     
     
       50. A method according to claim 49, wherein a total weight of the toner particles in the toner particle layer on the surface of the developer carrying sleeve and the toner particles on the surfaces of the magnetic particles at the developing station is 4-40% of a weight of the magnetic particles in the developing position. 
     
     
       51. A method according to claim 47 or 48, wherein the chains of magnetic particles have a resistivity of  15  -10 6  Ohm-cm. 
     
     
       52. A method according to claim 51, wherein the magnetic particles have an average particle size of 30-100 μm. 
     
     
       53. A method according to claim 52, wherein said magnetic particles are ferrite particles coated with resin. 
     
     
       54. A developing method, comprising: forming a layer of a developer containing toner particles and magnetic particles on a surface of a cylindrical sleeve;   carrying said developer layer to a developing position where a surface of a rotatable electrostatic latent image bearing drum for baring an electrostatic latent image is opposed with a clearance to the surface of the cylindrical sleeve;   forming chains of the developer by stationary magnetic field generating means in said cylindrical sleeve at the developing position, wherein the chains extend towards and contact the drum;   forming an electric field having alternately changing directions to develop the latent image with the toner particles at the developing position, wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing member and the developer carrying member at the developing position is 1.5- 30%.   
     
     
       55. A method according to claim 54, wherein from 0.5×10 -2  -5×10 -2  g/cm 2  of developer is carried on the developer carrying sleeve including the toner particle layer, the toner particles on the surfaces of the magnteic particles and the magnetic particles. 
     
     
       56. A method according to claim 55, wherein a total weight of the toner particles in the toner particle layer on the surface of the developer carrying sleeve and the toner particles on the surfaces of the magnetic particles at the developing station is 4-40% of a weight of the magnetic particles in the developing position. 
     
     
       57. A method according to claim 55 or 56, wherein the chains of magnetic particles have a resistivity of 10 15  -10 6  Ohm-cm. 
     
     
       58. A method according to claim 57, wherein the magnetic particles have an average particle size of 30-100 μm. 
     
     
       59. A method according to claim 58, wherein said magnetic particles are ferrite particles coated with resin. 
     
     
       60. A developing apparatus for developing an electrostatic latent image on a rotatable electrostatic latent image bearing drum, comprising: a container for containing a developer which contains toner particles and magnetic particles;   a rotatable developer carrying cylindrical sleeve, opposed to the electrostatic latent image bearing drum, for forming a developing position for supplying the toner particles to the latent image bearing member and for carrying a layer of the toner particles formed on a surface of the cylindrical sleeve and magnetic particles retaining on their surfaces the toner particles from said container to the developing position;   first stationary magnetic field generating means disposed in the cylindrical sleeve for generating a magnetic field to contact the magnetic particles to the latent image bearing drum at the developing position;   a non-magnetic member disposed upstream of the developing position with respect to movement of the surface of said cylindrical sleeve and spaced apart from the surface of said cylindrical sleeve for regulating the developer carried to the developing position;   second stationary magnetic field generating means, disposed in the cylindrical sleeve wherein a maximum magnetic field generating portion of the second magnetic field generating means is disposed upstream of said non-magnetic member with respect to the movement;   a magnetic member disposed adjacent said non-magnetic member, wherein a clearance between the magnetic member and cylindrical sleeve is larger than a clearance non-magnetic field generating portion of the second magnetic field generating means is disposed upstream of said magnetic member with respect to the movement, and wherein said second magnetic field generating means imparts a magnetic field to said magnetic member; and   electric field forming means for forming, at the developing position, an electric field having alternately changing directions to develop the latent image by the toner particles in said layer and on the surface of said magnetic particles.   
     
     
       61. An apparatus according to claim 60, wherein said magnetic member is disposed upstream of aid non-magnetic member with respect to the movement. 
     
     
       62. An apparatus according to claim 61, wherein an angle, seen from the center of said sleeve, between said non-magnetic member and said maximum magnetic field generating portion of said second magnetic field generating means is 5°- 25°. 
     
     
       63. An apparatus according to claim 61 or 62, wherein a clearance between said non-magnetic member and said sleeve is 50-600 microns. 
     
     
       64. An apparatus according to claim 60 or 61, wherein a volumetric ratio Vd of the total volume of the magnetic particles existing at the developing position to a volume of space defined by the surface of the electrostatic latent image bearing drum and the developer carrying sleeve at the developing position, is 1.5-30%. 
     
     
       65. An apparatus according to claim 61, further comprising a developer circulation limiting member disposed adjacent to and upstream of said magnetic member with respect to the movement and cooperable with said cylindrical sleeve to form a clearance therewith having a sectional area gradually decreasing toward said non-magnetic member from an upstream side, wherein the limiting member is on a line connecting the center of the sleeve and a maximum magnetic field generating portion of said second magnetic field generating means.